The present invention relates to a heater structure for an aquarium, and more particularly to an electronic heater structure in which the temperature controlling circuit is integrated and received in the tube body. Except the heating wire, the temperature controlling circuit itself will not generate high heat and emit electro-magnetic interference so that the water temperature can be accurately detected.
A conventional aquarium heating tube includes a glass tube in which an alloy heating wire and a controlling circuit are enclosed. The opening of the glass tube is watertightly sealed by a cap. The controlling circuit includes a bimetal plate. An adjustment rod abuts against a bending section of the bimetal plate so that in the case that the water temperature is too low, the contacts of the bimetal plate engage each other to power on the heating wire and adjust the water temperature. When the water temperature reaches a certain value, the contacts jump apart to cut off the power so as to maintain the temperature within a substantially constant range. Such structure employs mechanical thermal expansion and contraction properties to achieve the temperature control so that the temperature controlling effect has a great error up to 1 to 2.degree. C. In use, the adjustment rod must be frequently adjusted and aligned. Such heating tube has poor quality and low price.
FIG. 6 shows an electronic heating tube in which an electronic measure is used to control and adjust the temperature. The accuracy of the temperature controlling can reach 0.3.degree. C. so that once rectified, the temperature of the aquarium can be reliably maintained in a constant state. In use, it is unnecessary to frequently adjust the adjustment rod. Such heating tube has good quality. However, such structure still has some shortcomings as follows:
1. In such electronic temperature controlling circuit, the adjustment is achieved by a TRIAC transistor which will generate a noise when powered on. The noise will cause EMI interference with general electric appliances. PA1 2. The electronic temperature controlling circuit has a large volume and thus can hardly be received in the tube. The controlling part must be fixed outside the tube in a separate housing connected to the tube via a wire. Therefore, the adjustment cannot be performed conveniently as adjustment of the traditional heating tube. PA1 3. The temperature detection is achieved by a thermosensitive resistor and the silicon controlling elements will generate heat themselves. Therefore, in the case that they are sealed in the tube together with the thermosensitive resistor, a serious error in temperature sensing will take place to affect the accuracy of the temperature controlling. Therefore, in order to achieve better accuracy of temperature controlling, the temperature detection parts are fixed outside the tube and connected to the tube via a wire.
In addition, FIG. 7 shows another electronic heating tube in which the thermosensitive resistors are sealed in the upper cap to save cost and facilitate processing. However, the heating tube is not equipped with good isolation measure so that the heat generated by the heating wire will affect the accuracy of the thermosensitive resistors via radiation and air convection. Therefore, error will inevitably take place. Moreover, the projecting chamber disposed on the cap actually is not free from the wrapping of the plastic material of the cap and can hardly effectively get close to the water level. Therefore, it is impossible to achieve an accurate temperature controlling effect.